It is estimated that as many as 150,000 women per year in the United States undergo a trial of labor after a previous cesarean section. With continuing efforts to reduce the cesarean section rate in the United States, this number is likely to continue to rise dramatically. Although this procedure is generally believed to be safe, there is a small risk of uterine rupture in these women. Uterine rupture is a potentially catastrophic complication for both mother and neonate, with estimates of maternal mortality as high as 1.6% and estimates of neonatal mortality as high as 25%. The existing data on the incidence of uterine rupture are suspect, mainly due to imprecise and non-quantitative case definitions. In contrast, there is evidence to suggest that the incidence of uterine rupture in this group is rising, possibly due to changing indications and management of such patients. Additionally, there has been only one study to evaluate risk factors for uterine rupture. That study focused mainly on the labor characteristics of such patients, and did not attempt to predict which patients are at greatest risk for rupture. The Specific Aims are to: 1) determine the incidence of uterine rupture in a cohort of patients with a history of a prior cesarean section who are subsequently attempting a vaginal delivery; 2) define risk factors for the occurrence of uterine rupture in women with a prior cesarean section who are attempting a vaginal delivery; this will be addressed by examining a case-control study nested within the cohort; the relationship between patient parameters and other clinical factors and the risk of uterine rupture will be assessed. 3) utilize the results of the case-control study to develop a clinical predictive index to define groups of patients at high risk of uterine rupture among women with a prior cesarean section, but who are now attempting a vaginal delivery. This predictive index is intended to help clinicians decide whether to offer a patient with a prior cesarean section an attempt at a vaginal delivery, based on the risk of uterine rupture to that patient. 4) define factors associated with the decision by which a patient is offered a trial of labor, by utilizing a case-control design. The methods to be employed include: 1) performance of a retrospective cohort study to determine precisely the incidence of uterine rupture in women attempting a trial of labor after a prior cesarean section; 2) patients undergoing trials of labor after a prior cesarean section will be identified by an ICD code for "previous cesarean delivery, delivered" in the years 1990-1996; 3) the medical records both of cases of uterine rupture and of a random sample of non-cases will then be reviewed in detail and data from these groups will be compared. The primary analyses of these case-control data will include unadjusted analysis and multivariable explanatory models, to provide insight into the etiology of uterine rupture. Then, the data from the case-control study will be used to develop a clinical predictive index, in order to identify women at high risk of uterine rupture. This predictive rule will then be validated in a separate patient sample. The information in the predictive model is expected to be useful to physicians to select appropriate patients for a trial of labor after a prior cesarean section.